1. Technical Field
This invention relates to cordless telephones and more particularly to a method and apparatus employed in a cordless telephone for providing increased functionality and for extending the useful battery life of portable units in such telephone.
2. Description of the Prior Art
The Federal Communications Commission (FCC) recently promulgated rulings in the utilization of spread spectrum systems, including a frequency hopping system. These rulings now allow suppliers to produce improved cordless telephones which provide users much greater freedom and mobility than is available with conventional cordless telephones. Frequency hopping systems spread their energy by changing, or hopping the center frequency of the transmission many times a second in accordance with a pseudo-randomly generated list of communication channels. The result is a significantly higher signal to noise ratio than may be achieved by conventional techniques such as amplitude modulation that uses no bandwidth spreading.
These improved cordless telephones provide security naturally from an eavesdropper listening in on a conversation simply because of the spread spectrum/frequency hopping transmission technique employed by these telephones. Examples of such improved cordless telephones are described in U.S. Pat. No. 5,323,447 which issued to M. E. Gillis et al. on Jun. 21, 1994, U.S. Pat. No. 5,353,341 which issued to M. E. Gillis et al. on Oct. 4, 1994 and U.S. Pat. No. 5,463,659 which issued to W. J. Nealon et al. on Oct. 31, 1995.
Although these improved cordless telephones give users much more freedom and mobility than conventional cordless telephones, high battery drain current limits the period of time for reliable operation of the portable units while located remote from a charging cradle or station. In order to extend this time and yet insure reliable operation for an extended period, one specific arrangement, disclosed in U.S. Pat. No. 4,731,814 and issued to W. R. Becker et al. on Mar. 15, 1988, reduces the battery drain current in the portable unit when the telephone is not in use and the portable unit is on-hook, i.e., no telephone call is in progress. Operation of the portable unit is through a process wherein power to the transmitter in the portable unit is removed and power to the receiver and other selected circuitry in the portable unit is cycled on and off to minimize power consumption when the portable unit is located remote from its charging cradle and also monitoring for a telephone ring signal from the base unit.
In order to provide longer standby and talk times, another specific arrangement described in U.S. Pat. No. 5,519,762 and issued to R. A. Bartlett on May 21, 1996 provides adaptive power cycling for a cordless telephone. With this approach, each portable unit has a variable power cycle which depends on that portable unit's specific usage. Thus, each portable unit in the system adjusts its power cycle based on the length of time since it last communicated with the base unit or another portable unit.
While these types of arrangements have been generally satisfactory in the past, consumers are now expecting ever increasing talk times from those portable units employed with the improved cordless telephones. Although ample technical challenges yet remain in the design of cordless telephones suitable for operating in a frequency hopping system, it is nevertheless desirable to provide a cordless telephone that provides the desired functionality, including increased battery life for a portable unit, while operating in such a system.